Etching end point judging device

ABSTRACT

An etching end point judging device which uses emission spectroscopy for dry etching. The device includes an AND converter for obtaining time series data of emission intensity of a specific wavelength produced during etching, a first digital filter for performing smoothening of the time series data, a differential operator for obtaining a differential coefficient of the smoothened time series data, a second digital filter for smoothening the calculated differential coefficient of the time series data, and a discriminator for judging the etching end point by comparing said smoothened differential coefficient with a value set beforehand.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a Divisional application of U.S. applicationSer. No. 09/452,174, filed Dec. 1, 1999, the subject matter of which isincorporated by reference herein.

BACKGROUND OF THE INVENTION

[0002] This invention relates to an etching end point judging method andto devices suitable for detecting etching processing end points in aplasma discharge process through use of emission spectrometry; and, theinvention also relates to an insulation film etching method using theetching end point judging method and the etching processing detectiondevices. The insulation films include a silicon oxide film (referred toas an oxide film henceforth) and a low-k film consisting of a materialhaving a low dielectric constant.

[0003] During dry etching processing of a semiconductor wafer, theemission intensity at a specific wavelength in plasma light changesaccording to the etching progress of a specific film. A conventionalsemiconductor wafer etching end point detection method is available todetect changes in the emission intensity at a specific wavelength fromplasma and detect an etching end point of a specific film based on thedetection result during dry etching processing. In this method,detection errors caused by an irregularity in the detected waveforms dueto noise must be prevented. In this regard, methods for improving thedetection accuracy of the emission intensity changes are disclosed inJapanese Non-examined Patent Publication No. 61-53728 and No. 63-200533.In Japanese Non-examined Patent Publication No. 61-53728, noise isreduced by a method of moving averages, and in Japanese Non-examinedPatent Publication No. 63-200533, noise is reduced by noise squareapproximation processing.

[0004] In an etching end point judging device that judges an etching endpoint of a wafer which is being processed by etching with a plasmadischarge using emission spectrometry, the detection signal becomesweaker after each wafer processing due to attachment of deposits. Asdescribed in Japanese Non-examined Patent Publication No. 63-254732,detection signals can be corrected by changing the gain value and offsetvalue of the detection signal for stable etching end point detection.Alternatively, as described in Japanese Non-examined Patent PublicationNo. 04-57092, without the addition of a gain and offset adjustmentfunction, the detection signal that was fetched to the opticalconversion method can be adjusted to a set value for stable etching endpoint detection.

[0005] With the recent progress toward downsizing and high integrationof semiconductors, the opening rate (area to be etched) on asemiconductor wafer is becoming smaller and the emission intensity at aspecific wavelength that is fetched by a light detector of an opticalsensor is becoming weaker. As a result, the level of the sampling signalfrom a light detector is becoming lower, making it difficult to detectan etching end point correctly based on a sampling signal from the lightdetector.

[0006] As the size of a semiconductor device becomes smaller, theelectrical capacity of the silicon oxide film used for insulationbetween wires increases, and the signal loss between wires can no longerbe ignored. As a solution to this problem, a method of reducing theelectrical capacity between wires is being developed in which a lowdielectric constant material is used as the insulation material betweenwires. Various materials have been developed as candidates for lowdielectric constant materials (referred to as low-k materialshenceforth). As described on page 74 in the monthly magazineSemiconductor World, 1998, No. 11, these materials include FSG (k=3.3 to3.6), HSQ (k=2.9 to 3.1), and Xerogel (k=2.0 or less) as inorganic low-kfilms, SiLk (k=2.6), BCB (k=2.6), FLARE (k=2.8), and PAE (k=2.8) asorganic low-k films, and organic SOG (k=2.8 to 2.9) and HSG (k=2.9).

[0007] In addition, a damascene process that enables wiring using copperthat has a lower electric resistance than conventional wiring materialsis being developed through use of a flattening process (CMP) based onchemical and mechanical corrosion technology.

[0008] In the damascene process, the main method is the dual damascenemethod in which a wiring groove is formed by plasma etching afterforming a low-k film, which is used as an insulating material betweenwires and layers, and then a contact hole is formed between the twolayers for permitting electrical connection to the lower layer. Theprocess of the dual damascene method differs depending on whether acontact hole or a groove is etched initially. Currently, various methodsare being examined. In either case, grooves and contact holes must beformed on low-k films using plasma etching. By using a process of highprecision plasma etching with fewer stages, the yield can be enhancedand the cost can be reduced, thereby substantially enhancing thecharacteristics of plasma etching (etching process and performance).

[0009] However, in the currently manufactured damascene structure, anetching stopper layer is formed by inserting a silicon nitride film onthe boundary between the groove and the hole provided on the low-k film.Consequently, the need for a stopper layer formation process and theincrease of the dielectric constant of the film due to insertion of astopper layer become problems. There will be no problem if thedielectric constant of the stopper layer is low. However, to satisfyrequirements regarding an etching selection ratio and adherence with thelow-k film, a silicon nitride layer is currently being used.

[0010] Even if a stopper layer is inserted, the film thickness cannot beincreased in terms of an increase of the dielectric constant. Therefore,accurate judgment is necessary regarding whether etching has progressedto the stopper layer. Although the ordinary end point judging system candetect this, more accurate judgment is required. The better method is toemploy a structure that does not require insertion of a stopper layer,however, such etching becomes difficult under current conditions.

[0011] In an insulating film etching device, a change with the passageof time is detected, such as deterioration of the etching speed, as theetching is repeated. In some cases, the etching may stop. This problemmust be solved. In addition, it is important to monitor fluctuations inthe etching speed with time for stable operation; however, in theconventional method, the end point judgment time is simply monitored.Moreover, when the etching duration becomes short, such as about 10seconds, the judgment preparation time and the judgment interval mustalso be reduced in the end point judgment method. However, in theconventional method, a sufficient measure to address this requirementhas not been taken. For an insulation film, as the etched area is often1% or less, the changes in the plasma emission intensity from theresidue that is generated as a result of etching is small. Consequently,an end point judging system that can detect very small changes isnecessary. However, a practical system at a reasonable price is notavailable at present.

[0012] To resolve the problem of drift in a lithography position duringetching for forming a contact hole on an insulation film, aself-alignment contact technology has been developed. In the end pointjudgment used in this technology also, since the etched area of the lastcontact section is small (1% or less), a system having a high detectionsensitivity for plasma emission intensity changes is necessary; however,the end point judging system presently available does not satisfy therequirements for high precision and a reasonable cost.

SUMMARY OF THE INVENTION

[0013] The primary object of this invention is to provide an etching endpoint judging method and a detection device that are capable of stabledetection of etching end points of semiconductor wafers even for asemiconductor wafer having a low opening rate.

[0014] The secondary object of this invention is to develop a method ofobtaining high-quality etching results by detecting plasma etching endpoints of semiconductor thin films using an end point judging systemthat can detect very small changes of plasma emissions and also canmeasure the data in a short time during plasma processing, inparticular, plasma etching processing.

[0015] Another object of this invention is to provide an etching endpoint judging method and a detection device that can eliminate any endpoint judging detection errors when a pulse type noise is induced in anemission intensity sampling signal (for instance, instantaneoustermination of discharge power or an abnormality caused by modulation ofthe emission intensity due to a sudden change of the plasma state causedby an instability).

[0016] Another object of this invention is to provide an etching endpoint judging method and a detection device that can easily displayoccurrences of plasma discharge abnormalities as history data.

[0017] Another object of this invention is to provide an etching methodfor enabling high-precision etching in a damascene process and aself-alignment process using a method or system that can measure, with ahigh precision, end points of an insulation film etching process of asemiconductor device.

[0018] Another object of this invention is to prevent etching faults inan etching device, which are caused by changes in time, by determiningthe etching speed through measurement of the etching time required toetch up to the stopper layer in the damascene process or up to theinsulation film on the gate in the self-alignment contact process, andmonitoring the fluctuations. By judging the correct time required forreaching the stopper layer in the damascene process, corrosion of a thinsilicon nitride layer can be retarded, thereby improving the realselection ratio.

[0019] Another object of this invention is to control deterioration ofdevice performance by retarding excessive advancement of etching on thebedding layer by judging the correct etching ending time, since etchingends in a short time, in the process for removing the silicon nitridelayer that was formed on the bedding in a damascene process or aself-alignment contact process.

[0020] An object of this invention is to provide an etching end pointjudging method for use in dry etching. The method includes a step ofreducing noise by processing input signal waveforms through a firstdigital filter, a step of finding a differential coefficient (primary orsecondary) of a signal waveform through differential processing, a stepof obtaining a smoothed differential coefficient value by reducing thenoise component of the time series differential coefficient that wasobtained by the previous step, and a step of judging an etching endpoint by comparing the smoothed differential coefficient value and apreset value through discrimination.

[0021] Another object of this invention is to provide an etching endpoint judging method for judging an etching end point from time seriesdata of an emission intensity differential coefficient. The methodincludes a step of displaying a transition of time series data of thedifferential coefficient through a display method and adding the displayindicating an abnormality on the display of the time series data of thedifferential coefficient when an abnormality is detected.

[0022] Another object of this invention is to provide an etching endpoint judging device that uses emission spectrometry. The device isequipped with an AD converter for obtaining emission intensity timeseries data of a specific wavelength, a first digital filtering devicefor performing smoothing processing for the time series data, adifferential operation device for obtaining a differential coefficientof the smoothed time series data, a second digital filtering device forperforming smoothing processing for the time series data of thedifferential coefficient that was calculated, and a discriminationdevice for judging an etching end point by comparing the smoothingdifferential coefficient value and a preset value.

[0023] Another object of this invention is to provide an insulation filmetching method for judging an etching end point using the etching endpoint judging method described above in the etching of an insulationfilm containing a low-k film consisting of a silicon oxide film or a lowdielectric constant material.

[0024] This invention can provide a very stable method for judgingetching processing end points, since it enables accurate calculation ofemission intensity changes. In addition, in end point judgment thatincludes differential coefficient calculation processing, noise in thesampling signals from a light detector can be reduced effectively bysetting digital filtering processing before and after differentialcoefficient calculation processing, enabling stable and accurate endpoint judgment.

[0025] By setting coefficient correction processing in digital filteringprocessing in the former stage, differential coefficient calculationprocessing, and digital filtering processing of the latter stage, noiseof sampling signals from a light detector can be reduced effectively inthe case of an abnormality occurring during the etching processing,enabling stable and accurate end point judgment.

[0026] By drawing in a zero or the preset display position with aspecific color arrangement when an etching processing abnormality occursduring differential coefficient display, a high-quality device thatfacilitates abnormality monitoring during etching processing can beprovided.

[0027] This invention enables execution of a correct end point judgment,thereby providing the effect of setting a lower over-etching thanobtainable with time management etching. As a result, excessivecorrosion of the bedding layer can be controlled. Since this inventionreduces the over-etching duration, improvement of the throughput can beexpected. Since changes in the passage of the etching time can bemonitored, an etching device abnormality can be detected at an earlystage, enabling prevention of a large number of etching faults.

[0028] This invention enables determination of a correct sense voltagevalue for the target output value of a photo-multiplier by using a sensevoltage value for a target output voltage value of a photo-multiplierthrough a relational expression. Therefore, even for a semiconductorwafer having a small opening rate, the etching signals used for stabledetection of etching end points of semiconductor wafers can becontrolled to a specified value repeatedly without any irregularitybetween wafers.

[0029] By using the end point judging system of this invention, judgmentcan be prepared in a short time and small plasma emission intensitychanges can be detected. Therefore, this system can be applied to endpoint judgment of insulation film etching of a small etched area.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1 is a block diagram of an etching end point judging devicethat represents an example of this invention.

[0031]FIG. 2 is a flow diagram showing an example of the processingprocedure employed in the device shown in FIG. 1.

[0032]FIG. 3 is a flowchart of the offset control and gain correction inthe processing procedure shown in FIG. 2.

[0033]FIG. 4 is a graph which shows an example of an emissionfluctuation measurement result when offset control and gain control arenot performed.

[0034]FIG. 5 is a graph which shows an example of an emissionfluctuation measurement result when offset control and gain controlaccording to this invention are performed.

[0035]FIG. 6 is a graph which shows multiplication rate characteristicsof a photo-multiplier.

[0036]FIG. 7 is a flowchart of sense voltage and gain correctionprocessing.

[0037]FIG. 8 is another flowchart of sense voltage and gain correctionprocessing.

[0038]FIG. 9 is a diagram which shows the calculation flow of smootheddifferential coefficient time series data Di according to thisinvention.

[0039]FIG. 10 is a graph which shows the original waveform and processedwaveform when the digital filter method of the device shown in FIG. 1 isnot used.

[0040]FIG. 11 is a graph which shows the original waveform and processedwaveform of the device shown in FIG. 1.

[0041]FIG. 12 is a graph which shows the original waveform and processedwaveform when noise occurs according to the processing procedure shownin FIG. 9.

[0042]FIG. 13 is a graph which shows the processing procedure in thesecond implementation example of the calculation flow of smootheddifferential coefficient time series data Di according to thisinvention.

[0043]FIG. 14 is a waveform diagram which shows the original waveformand processing waveform of the implementation example shown in FIG. 13.

[0044]FIG. 15 is a flow diagram of a second example of the processingprocedure used in the device shown in FIG. 1.

[0045] FIGS. 16 to 16(f) show an example of a self-alignment dualdamascene process.

[0046] FIGS. 17(a) to 17(e) show an example of a damascene process thatprocesses a groove first.

[0047] FIGS. 18(a) to 18(e) show an example of a damascene process thatprocesses a hole first.

[0048] FIGS. 19(a) to 19(f) show an example of a process when a boundarylayer between a hole and a groove is not formed.

[0049] FIGS. 20(a) and 20(b) show an example of the process when a low-kfilm structure is introduced.

[0050]FIG. 21 shows, as an application example of this invention toself-alignment contact technology, a pre-etching cross-section of theself-alignment contact.

[0051]FIG. 22, as shows an application example of this invention toself-alignment contact technology, a post-etching cross-section of theself-alignment contact.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0052] The following section describes a first example of thisinvention. FIG. 1 will be used to explain etching of a semiconductorwafer. In FIG. 1, the configuration of a semiconductor wafer etchingdevice 1 and etching end point detector 10 is outlined.

[0053] In the etching device 1, the etching gas introduced into etchingchamber 2 is transformed to a plasma after being decomposed by microwavepower, and a semiconductor wafer is etched by the plasma. Etching endpoint detector 10 detects plasma light that is generated in the etchingchamber 2 during semiconductor wafer etching processing and performs endpoint judging processing based on the detection result. Etching endpoint judging detector 10 is equipped with optical detector 11, offsetcircuit (addition circuit) 15, gain circuit (multiplication circuit) 16,AD converter 17, digital filter circuit 18, differential coefficientoperation circuit 19, digital filter circuit 20, RAM 21, judgmentcircuit 22, DA converter 23, and CPU 30. The programs corresponding toauto offset/auto gain control processing, sense voltage settingprocessing, sampling processing that includes smoothing processing, andend point judging processing are stored in ROM 31. These programs areexecuted by CPU 30. Reference numeral 32 denotes an external storageunit and reference numeral 33 denotes an input/output device.

[0054] Optical detector 11 detects the emission of a specific wavelengthfrom the plasma that was generated in etching chamber 2 during etchingprocessing using a spectroscope 12 and supplies the emission to aphoto-multiplier 13 via an optical fiber. The emission intensity of thespecific wavelength that was fetched is transformed to a currentdetection signal by photo-multiplier 13 according to the emissionintensity and is converted to a voltage signal by IV converter 14. Thevoltage signal converted by IV converter 14 is processed by differentialcircuit (offset) 15 and amplification circuit (gain) 16.

[0055] The signal output by AD converter 17 as a sampling signal isstored in RAM 21 as time series data yi. Digital filter circuit 18performs smoothing processing for time series data yi and stores thedata in RAM 21 as smoothed time series data Yi. Differential coefficientoperation circuit 19 calculates time series data di of the differentialcoefficient value (primary differential value or secondary differentialvalue) from the smoothed time series data Yi and stores the data in RAM21. Digital filter circuit 20 performs smoothing processing fordifferential coefficient value time series data di and stores the datain RAM 21 as smoothed differential coefficient time series data Di.Judgment circuit 22 compares the smoothed differential coefficient valuewith a preset value and detects an etching end point using the rawwaveform signal or operation waveform signal.

[0056] The detection signal of the raw waveform signal or operationwaveform signal is weakened by each wafer processing performed inetching chamber 1 due to deposits attached thereon, changing the endpoint detection condition for each wafer. By changing the sense voltagefor controlling the output voltage of photo-multiplier 13 and the gainof amplification circuit 16, the detection signals of all wafers can bemade identical, enabling etching end point detection under the samecondition.

[0057] As shown in FIG. 1, etching end point judging detection device 10of this invention is equipped with the functions of auto offset/autogain control processing, sense voltage setting processing, samplingprocessing including smoothing processing, and end point judgingprocessing. These functions will be explained with reference to FIG. 2.

[0058] When etching processing starts, a sampling start instruction isissued (100). The emission intensity of the specific wavelength thatchanges according to the etching progress is detected by a lightdetector as a light detection signal of the voltage corresponding to theemission intensity. The light detection signal is converted to a digitalvalue by an AD converter as sampling signal li and is stored in RAM.Time series data y_(i) (101 ) of the following expression (1) isdetermined by auto offset/auto gain control at A/D conversion.

y _(i) =l _(i) +d _(i)  (1)

[0059] l_(i) is a low gain at offset zero and d_(i) is a high gain atoffset zero.

[0060] The next step is to check whether the time is within the sensevoltage setting time of light detector 11 (102). If the time is withinthe voltage setting time, the system advances to sense voltage settingprocessing (103). When the time exceeds the sense voltage setting time,the system checks to see if time series data yi is the present value,for instance 4 V or higher (106). When time series data yi is 4 V orhigher, the system changes the sense voltage to the value for which timeseries data yi was preset, such as 0.6 V or less (107).

[0061] That is, the system reduces noise through the digital filter ofthe first stage and obtains smoothed time series data (108). Then, thesystem obtains differential coefficient (primary or secondary) di of thesignal waveform through differential processing (109). The systemobtains smoothed differential coefficient time series data Di that wasgenerated by reducing the noise component of the time seriesdifferential coefficient described above using the digital filter of thesecond stage (108). The system calculates (D_(i)−L)*(D_(i-1)−L) usingthe end point judging level L that was preset (111).

[0062] By judging the sign (negative or positive) of(D_(i)−L)*(D_(i-1)−L), the system performs end point judging processingof the etching process. If the sign is negative, the system judges theresult as true and terminates the sampling (113). If the sign ispositive, control is returned to the first step 101.

[0063] Sense voltage setting processing (103) calculates a sense voltagethat makes smoothed time series data yi to be preset voltage ys, usingsmoothed time series data yi and the dark current value of the detector(104). The processing also checks to see whether smoothed time seriesdata yi is preset voltage ys as shown in the following expression (2) inthe sense voltage that was set. If not, the sense voltage is changed(105) and control is returned to the first step 101.

yi−ys0≦ys≦yi+ys0 ys0=0.1 V  (2)

[0064] This invention enables optimization of optical signal intensityby using the auto sense feature, that is, the characteristics of thephoto-electric element. As a result, the light signal intensity can beset to the optimum level at a high speed. This auto sense featureprovides a substantial effect for step etching.

[0065] The detection precision of sampling signal 1 _(i) is restrictedby the gain of amplification circuit 16 and the resolution of the ADconverter 17. For instance, when an amplification circuit of gain 1 andan AD converter of restricted voltage □10 V and a resolution of 12 bitsare used, the minimum resolution voltage is 4.88 mV and the fluctuationdetection precision of the light detection signal of about 2.5 V is 0.2%(0.0488 mV/2.5 V), which is not an acceptable detection precision level.To solve this problem, the detection precision is enhanced bycontrolling the offset value of the differential circuit 4 and the gainvalue of amplification circuit 5 that were described above.

[0066]FIG. 3 is a flowchart of offset value control of the differentialcircuit 15 and gain value control of the amplification circuit 16. Whena sampling start instruction 100 is issued, the system sets the offsetvalue of the differential circuit 15 to zero (1010) and the gain valueof the amplification circuit 16 to 1 (1011). The system fetches thesampling signal I that was converted to digital data from a lightdetection signal by AD converter 17 (1013). The system stores samplingsignal l_(i) in RAM 21 (1014).

[0067] Then, CPU 30 sets the offset value of the differential circuit 15from DA converter 23 using sampling signal value l_(i) described above.CPU 30 then sets the gain value of the amplification circuit 16 to thepreset value (1016). In the next step, the light detection signal of thelight detector 11 is converted to digital data by the AD converterthrough amplification circuit 16, and sampling signal □l_(i); isobtained (1017). In the next step, CPU 30 stores the value produced byadding sampling signals li and □l_(i) that have been stored, in RAM 21as time series data yi (1018). CPU 30 performs arithmetic operationsbased on time series data yi that is stored and performs a signalintensity comparison operation and a differential processing operation.

[0068] Auto offset control according to this invention has the followingfeatures.

[0069] 1) Obtains an absolute value of an input signal from the sum ofan offset value and a differential amplification value.

[0070] 2) Obtains an offset value for an absolute value of an inputsignal and detects a differential amplification value from the offsetvalue.

[0071] 3) Detects an offset value by setting the gain of the ADconversion to a low gain.

[0072] 4) Truncates one bit of the offset value to the differentialcircuit according to the resolution of the DA converter and sets thevalue.

[0073] Auto offset control according to this invention has features inits method of maximizing the resolution of the AD converter by using adifferential amplification circuit of an AD converter.

[0074] In the first step, an approximate absolute value of the signalvoltage is obtained by processing an input signal waveform through ADconversion at low gain operation. The next step is to obtain an inputvoltage to a differential amplification circuit of the AD converter,considering the resolution of the DA converter (truncating 10 mV andless). Input voltage V₀ to the AD converter that was obtained in theprevious step is output to a DA converter.

[0075] The differential waveform of the input signal is processed by ADconversion at high gain operation, and a high-precision differentialsignal voltage V₁ is obtained. The next step is to compose the voltagevalues that were obtained in the previous 2 steps.

Voltage: V=V ₀ +V ₁

[0076] Auto offset control according to this invention enableshigh-precision AD conversion for changes of signal waveforms with thepassage of time. This means that signals of high input waveformintensity can be handled by measuring signal waveforms in a maximumconversion area measuring mode.

[0077] Bit quantified errors in the AD conversion can be reduced. Bitquantified errors in DA conversion can also be reduced. As a result ofdifferential amplification, the signal level that is output is reducedand the gain of the AD converter can be maximized, enablinghigh-precision measurement. High-precision measurement is also enabledfor values of input signal waveforms.

[0078] Offset control according to this invention can be applied to ADconversion processing of electric signals, such as bias signals,pressure signals, and flow signals, in addition to optical signals, suchas EPD. Auto offset control can also extend the dynamic range of an ADconverter.

[0079]FIG. 4 shows an example of emission fluctuation measurementresults of the conventional method that does not perform offset controland gain control. FIG. 5 shows an example of emission fluctuationmeasurement results when offset control and gain control according tothis invention are performed. The diagrams indicate an improvement inthe emission fluctuation detection precision from about 0.5% to about0.02% by application of this invention. Consequently, the differentialcoefficient time series data that is used for judging an end point canbe obtained with a high precision, enabling stable end point judgment ofthe etching processing. Time series data obtained by this invention iszero when there is no plasma emission; and, when etching processing isperformed, time series data yi has a value greater than zero. Therefore,to perform arithmetic operations based on the time series data yi thatwas obtained, no special zero division avoidance processing is required,thereby simplifying the end point judging processing flow and reducingsoftware processing errors.

[0080] Sense voltage setting processing will be explained below.

[0081] By changing the sense voltage of the photo-multiplier 13 throughDA converter 23 in FIG. 1, the output voltage of the photo-multiplier 13can be controlled. FIG. 6 shows the multiplication rate characteristicsof photo-multiplier 13. An exponential relationship is established foroutput voltage l of high-voltage multiplier 13 to high voltage Hv ofphoto-multiplier 13 and the relation is characterized in the followingexpression 3.

l=Hv ^(a) (For instance a=7.5)  (3)

[0082] When the high voltage Hv of photo-multiplier 13 cannot bedirectly obtained, the voltage can be obtained by converting sensevoltage V, that is controlled by the CPU, using the following expression(4).

Hv=50 □V+400  (4)

[0083] Therefore, by using the relationship of expression 4 inexpression 3, the sense voltage V can be calculated for obtaining anexpected output of photo-multiplier 13 for a certain emission amount.This relationship can be expressed by expression 4 and expression 5.

V ₁ =Hv ₀/50*Exp(1/a □ Log(l ₁/(l ₀ −l _(d)))−8 (Hv ₀=50 □ V ₀+400)  (5)

[0084] l₁ is the target output voltage of photo-multiplier 13 and V₁ isthe sense voltage at that time, l₀ is the initial output voltage of thephoto-multiplier, ld is the output voltage of the dark current of thephoto-multiplier, and V₀ is the sense voltage at that time.

[0085] A photo-multiplier contains a dark current, and, when the sensevoltage is low, the dark current imposes a substantial influence on theoutput voltage of the photo-multiplier. For instance, l₀ is the initialoutput voltage of the photo-multiplier, and, when the sense voltage atthe time is very low, a correct sense voltage can be obtained bysubtracting the dark current from output voltage l₀ of thephoto-multiplier as shown in expression 5.

[0086] Dark current is measured after a wafer is delivered to a chamberand before a plasma is generated. Alternatively, the dark current may bemeasured when a wafer is not delivered to a chamber.

[0087] By setting sense voltage V₁ that was obtained by the methodindicated above, a required output voltage of photo-multiplier 13 can beoutput. The gain of amplification circuit 16 is normally amultiplication of a fixed value.

[0088] There is a limit in a sense voltage; and, when a required outputvoltage l1 of the photo-multiplier is not output even if a maximum sensevoltage value is set, normally the operation waveform signal isamplified by adjusting the gain to a fixed multiplication. For instance,if the required output voltage of the photo-multiplier is 2 V and theoutput voltage is 1 V when a maximum sense voltage value is set, theoperation waveform signals used for detecting an etching end point canbe matched by setting a gain of normal fixed value 2 for the gain ofamplification circuit 16 (gain correction).

[0089]FIG. 7 is a flowchart which shows an example of a process forobtaining a sense voltage value and a gain value. A waveform adjustmentimplementation instruction (1031) is issued to perform sense adjustmentand gain correction. The current sense voltage value (1032) and thecurrent raw waveform signal value (1033) are obtained by the waveformadjustment implementation instruction (1031). For instance, the sensevoltage value is obtained using number 3 and the sense voltage value andraw waveform signal value that were obtained as indicated above is 3, sothat the raw waveform signal becomes a target voltage value of 2 V(1034). The sense voltage value that was obtained by photo-multiplier 13from the DA converter is output (1035) and the system waits for the timerequired for the adjustment effects to appear (1036). Then, the systemcompares the target voltage value of 2 V and the current raw waveformsignal value and checks to see whether the error is within the standardvalue (1037). If the error is within the standard value, the systemterminates the sense adjustment (1038).

[0090] When the error is outside of the standard value, the system takesthe following steps. The system checks to see whether the sense voltagevalue that was output as indicated above exceeds the maximum value(1039). When the value exceeds the maximum value, the system comparesthe current raw waveform signal value and 2 V, multiplies the ratio bythe gain value that is normally set (gain correction) (1040) andterminates the sense adjustment and gain correction (1041). If the sensevoltage value that was output as indicated above is not the maximumvalue, the system increases or reduces the sense voltage value by 0.1 Vand outputs the sense voltage value (1042). The system checks to seewhether the time spent for sense adjustment is equal to or greater thanthe specified standard time. If the time is equal to or greater than thespecified standard time (1043), the system terminates the senseadjustment (1038), and if the time is less than the specified standardtime, the system returns control to the comparison between the targetvoltage value of 2 V and the current raw waveform signal value (1037),generating a loop. This loop operates, for instance, on a cycle of 0.1second.

[0091]FIG. 8 is a flowchart of another example of a process for a sensevoltage and gain correction. The basic processing flow is the same asthe processing flow shown in FIG. 7. When a sense value overflows (1039)or the time spent for sense adjustment exceeds a specified time (1043),the system obtains a ratio of the target raw waveform output voltage,for instance 2 V, to the current raw waveform signal value and storesthe result in memory.

[0092] The sense voltage value at that time is also stored in memory.The sense voltage output that was obtained is output to the sense valueand a fixed value is maintained as the gain. Although the value does notbecome the target value, which is 2 V, the sense adjustment isterminated by performing a computation based on the ratio between 2 Vand the current raw waveform signal value within the program of themicrocomputer (1038).

[0093] In the etching end point judging device used in thisimplementation example, since a correct sense voltage value can beobtained for the target output voltage of photo-multiplier 13, normally,the gain is a constant value, retarding the irregularity of the S/Nratio of each wafer by the gain and amplification irregularity. When asense value overflows, a target operation waveform can be obtained bycorrecting the value with the gain value or correcting the ratio betweenthe target output voltage and the current output voltage within theprogram to perform stable etching end point judgment.

[0094] The process flow for calculation of smoothed differentialcoefficient time series data Di will be explained in conjunction withFIG. 9. For digital filter circuit 18, a secondary Butterworth type lowpass filter is used. Smoothed time series data Yi is obtained from asecondary Butterworth type low pass filter using the followingexpression (6).

Y =b ₁ y _(i) +b2y _(i) +b ₃ y _(i)  (6)

[0095] Coefficient values “b” and “a” vary according to the samplingfrequency and the cutoff frequency. For instance, the following valuesare applied when the sampling frequency is 10 Hz and the cutofffrequency is 1 Hz.

a2=−1.143, a3=0.4128, b1=0.067455, b2=0.13491, b3=0.067455

[0096] Secondary differential coefficient time series data d_(i) iscalculated using the following expression (7), which uses a polynomialadaptation smoothing differential method of five values of time seriesdata Y_(i).

where, w ⁻²=2, w ⁻¹=−1, w ₀=−2, w ₁=−1, w ₂=2.  (7)

[0097] Calculation of the coefficients is described in the referencematerial: “Analytical Chemistry” 36 (1964) p.1627 by A. Savitzky, M. J.E. Golay.

D _(i) =b ₁ d _(i) +b ₂ d _(i-1) +b ₃ d _(i-2)  (8)

[0098] As an example for comparison, FIG. 10 shows the original waveformduring etching and secondary differential coefficient time series datadi that was obtained without using digital filter circuit 18 and digitalfilter circuit 20. The sampling time series data indicates that theetching end point is reached after 4.2 seconds from the start of theprocessing. Secondary diffusing time series data di of the differentialcoefficient value described above, smoothed differential coefficientdata Di can be obtained from the following expression (8) throughdigital filter circuit 7 (secondary Butterworth type low pass filter;however, the coefficients may be different from coefficients ‘a’ and ‘b’of digital filter circuit 5). Differential coefficient time series datad_(i) does not provide correct information for the judgment due to thenoise.

[0099]FIG. 11 shows the change of waveform when digital filter circuit18 and digital filter circuit 20 are used. As shown in the graph, noisein the smoothed secondary differential coefficient time series data Diis reduced, enabling detection of a clear etching processing end pointand stable end point judgment. In this way, noise of differentialcoefficient time series data can be reduced effectively by installingdigital filter circuit 18 and digital filter circuit 20 in differentialcoefficient operation circuit 19. Consequently, accurate differentialcoefficient time series data used for judging an end point can beobtained for achieving stable end point judgment of etching processing.

[0100] Other examples of this invention will be described below withreference to FIGS. 12 to 14. The same etching end point judging methodas that applied in the previous example is used. These examples showprocessing performed when an abnormality occurs during etching and whenpulse type noise is induced in the emission intensity sampling signal.FIG. 12 shows the secondary differential waveform that was calculatedaccording to the processing procedure in the previous example when pulsetype noise is induced during the time from the 2.5 second point to the3.5 second point. As shown in the graph, a large undershoot appears inthe smoothed time series data Yi, and, as a result, the smoothedsecondary differential waveform may become inaccurate.

[0101] In this example, abnormality processing is performed byinterrupting the calculation processing procedure for smoothed secondarydifferential coefficient time series data Di as shown in FIG. 13. Whenan abnormality occurs at i=m, smoothing processing is performed and thesmoothed time series data is assigned as Ym−1=ym and Ym=ym. At the stepi=m+1, Ym+1=ym+1 is assigned. Ym+3 of the step i=m+2 is obtained by thesecondary Butterworth low pass filter ring processing of digital filtercircuit 18 that was described above. At the step i=m +3, differentialvalue time series data dm+1 is calculated by differential coefficientoperation circuit 19 and the value is assigned in dm−1, dm, Dm−1, andDm.

[0102] Data is smoothed by using these values, and smoothed differentialcoefficient time series data Dm+1 is obtained. In steps from i=m+4,smoothed differential coefficient time series data is calculatedaccording to the processing procedure that is shown in FIG. 9. By thisabnormality processing procedure, the smoothed differential coefficienttime series data produced by eliminating the past time series datachange can be obtained from the third step following the abnormalityoccurrence.

[0103]FIG. 14 shows smoothed time series data Yi and smoothed secondarydifferential value waveform Di when the abnormality processing isapplied. On this graph, the time when the secondary differential passesthe zero point is more accurately determined (4.5 seconds when there isno pulse type abnormality and 4.56 seconds in this processing) than thegraph shown in FIG. 12. In this way, even if there are pulse typeemission intensity fluctuations, the influence of the fluctuations canbe reduced in a short time by performing abnormality processing.Consequently, accurate differential time series data used for judging anend point can be obtained, enabling stable end point judgment of etchingprocessing.

[0104] This invention enables reduction of noise (shot noise of a lightintercepting element, plasma light fluctuation, etc.) that is containedin a light signal by using digital filters and differential processing(S-G method).

[0105] According to the differential processing used by this invention,noise in an input signal waveform is initially reduced through the firstdigital filter. Then, a differential coefficient (primary or secondary)of the waveform is obtained using differential processing (S-G method).The noise components of the time series differential coefficientwaveform that were obtained in the previous step are reduced by thesecond digital filter.

[0106] In this invention, abnormality processing is performed when thedegree of change of the raw signal level exceeds the set valueinstantaneously (sampling interval).

[0107] That is, end point judging processing and display processing of adifferential value smoothed signal are interrupted and an abnormality isdisplayed on a display window. If the degree of change of the raw signallevel is a set value or less, the smoothed signal time series of thefirst step is reversed by two steps and the value of the current pointis assigned. The differential value signal and the differential valuesmoothed signal are reversed by as many steps as the number of degreesof the S-G method and the value at the current point is assigned.

[0108] According to the abnormality processing of this invention, anoise reduction level and a time response characteristic can be set bycontrolling the filter characteristics of the digital filter.

[0109] Since primary or secondary differential coefficients arecalculated using differential processing of the S-G method, differentialvalues of mathematically high precision can be processed at a highspeed. Noise components contained in differential values can also beremoved. (Substantial effects at integer processing)

[0110] In addition, high-speed differential processing can be performedafter an abnormality, and abnormality history data can be displayedeasily. Post-abnormality high-speed differential processing can also beperformed.

[0111] Abnormality processing according to this invention can alsoprocess abnormality flags from devices other than light signals. Unlikeanalog filter processing, digital filter processing can incorporate rawsignals in an operation processing at any time. The processing bringsabout substantial effects in step etching.

[0112] Another example of this invention relates to the display methodfor displaying information at steps m and m-1 where an abnormality hasoccurred in the previous example. Normally, differential coefficienttime series data is plotted on the monitor window of the display devicethat can monitor a state of etching processing any time during etchingprocessing. Diagrams such as those diagrams (b) in FIGS. 11 and 14 aredisplayed on the monitor window.

[0113] For smoothed differential coefficient time series data items Dm-1and Dm at the points of abnormality occurrence m and m-1, the correctedvalues are stored in RAM 9 and are used for obtaining the smootheddifferential coefficient time series data of the next step. However, onthe monitor window that displays a transition of the etching processing,the transition data is drawn on the zero or preset display position witha specific color arrangement. Since an etching abnormality is stored onthe monitor window, etching abnormality history data is kept in thedisplay device, enabling monitoring of abnormalities in real time.

[0114] Since the etching end point judging method of this example can beused to calculate emission intensity changes at high precision, theetching end point judging detection method can provide a very stablemethod for judging etching processing end points.

[0115]FIG. 15 is a flowchart of end point judging control, which isanother example of this invention. This feature judges an end point bycomparing two wavelengths.

[0116] When etching processing starts, the system issues a samplingstart instruction (100). Emission of a specific wavelength that changesaccording to the progress of etching is detected as a light detectionsignal. An AD converter converts the signal to a digital value assampling signal l_(i) and stores it in RAM. During A/D conversion, autooffset/auto gain control is performed (101 and 101′). Then, the systemchecks to see whether the time is within the sense voltage setting timeof light detector 11 (102 and 102′). If the time is within the voltagesetting time, control is passed to sense voltage setting processing(103). When the time exceeds the sense voltage setting time, the systemchecks to see whether time series data items yi and yi′ are 4 V orhigher (106 and 106′). When the time series data items yi and yi′ are 4V or higher, the sense voltage is changed to 0.6 V or less (107). Whenthe time series data items yi and yi′ are less than 4 V, control ispassed to smoothing processing.

[0117] In smoothing processing, initially, the ratio of time series datayi to yi′ is calculated (120). The noise is reduced by the digitalfilter of the first stage and smoothed time series data yi is obtained(108). Differential coefficient (primary or secondary) di of a signalwaveform is obtained by differential processing (S-G method) (109).Then, smoothed differential coefficient data Di is obtained by reducingthe noise components of the time series differential coefficientwaveform described above through the digital filter of the second stage(108). Using present end point judging level L, the result of(D_(i)−L)*(D_(i-i)−L) is obtained.

[0118] By checking a negative or positive sign of the result of(D_(i)−L)*(D_(i-1)−L), etching processing end point judging processingis performed (112). If the sign is negative, the system determines theresult to be true and terminates the sampling (113). If the result ispositive, the system returns control to the initial step (101).

[0119] An explanation of sense voltage setting processing (103) isomitted because this processing is the same as for FIG. 2.

[0120] By using the end point judging processing system of thisinvention that has been described, end points of an insulation filmetching process of semiconductor devices can be measured with a highprecision. Consequently, this method provides a method of implementingetching of a damascene process and a self-alignment process with a highprecision. A semiconductor manufacturing process using such a systemwill be explained below.

[0121] FIGS. 16 to 19(e) relate to typical damascene processes. FIGS. 16to 16(f) show a self-alignment dual damascene process; FIGS. 17(a) to17(e) show a process that processes a groove first; FIGS. 18(a) to 18(e)show a process that processes a hole first; and FIGS. 19(a) to 19(f)show a process where a boundary layer of a hole and a groove is notformed. The process shown in FIGS. 19(a) to 19(f), is an ideal processinvolving the least number of steps. However, since a boundary surfacebetween a hole and a groove is not formed, there are many etchingcharacteristic requirements, such as uniformity of etching speed withinthe wafer surface and repeatability. There are many problems that are tobe solved for employing this method for mass production.

[0122] The damascene process will be explained using the example ofself-alignment dual damascene processing shown in FIGS. 16 to 16(f). Toprocess a hole, a hole is made on resist 201 by exposure development.Under the resist, silicon nitride film 202, low-k film 203, nitridesilicon 204, and bedding 205, which is a wiring of the lower layer, areformed, as seen in FIG. 16. Initially, a mask corresponding to the shapeof the hole is formed on resist 201, as seen in FIG. 16(a), and then theopening section corresponding to the hole of resist 202 is formed onsilicon nitride film 202, which becomes a stopper layer. Resist 201 isremoved and low-k film 206 and oxide film 207 are formed on siliconnitride film 202, as seen in FIG. 16(b). This low-k film 206 becomes aninter-wire insulation film of the upper section.

[0123] Then, as seen in FIG. 16(c), resist mask 209 for processing agroove is formed on oxide film 207 through exposure development, andthen oxide film 207 and low-k film 206 are etched by plasma etching, asseen in FIG. 16(d). In this case, etching stops at silicon nitride layer202, which is the stopper layer equivalent to the bedding of low-k film206. When plasma etching is carried out using oxide film 207 as the maskof groove 208 and silicon nitride film 202 as the mask of the hole, hole210 is formed, as seen in FIG. 16(f). Finally, silicon nitride film 204is etched to effect contact with bedding 205. Then, wiring is formed byinserting a wiring material such as aluminum or copper in the openingsection (hole 210) and smoothing the upper section.

[0124] The problem in plasma etching of self-alignment dual damascene isthat the film thickness is reduced to several nm, since, if siliconnitride film 202 of the stopper layer is thick, the entire dielectricconstant becomes high. Since the film is very thin, a high selectionratio to the low-k film must be set. If the etching speed uniformity orrepeatability is low, over-etching must be applied excessively. This isalso the reason for setting a high selection ratio.

[0125] In accordance with this invention, after the etching times oflow-k films 206 and 203 are checked by the end point judging system andthe specified over-etching is applied, etching processing is terminated.In this case, the end points must be judged in a short interval,preferably an interval of about 0.1 s because the silicon nitride films202 and 204 of the stopper layer are very thin (several nm).

[0126] Since a correct time for etching on a low-k film so as to reachthe silicon nitride film can be judged by using the end point judgingmethod of this invention, unnecessary etching of silicon nitride 202 ofthe stopper layer can be prevented.

[0127] In accordance with this invention, the end point judging systemjudges the etching termination time, applies the specified over-etching,and ends the etching for silicon nitride film 204 that is formed onbedding 205. The method of this invention enables reduction of etchingon bedding 205. However, to realize this, the end point judging systemmust support a function for judging an end point in a short time asdescribed above, and, at the same time, the preparation time from thelighting of plasma and the start of etching to completion of preparationfor end point judgment must be short. The duration is preferably 5 s orless. If an end point can be judged in such a short interval, the amountof over-etching by etching end point judgment can be set and corrosionof the bedding 205 can be controlled even if etching terminates inaround 10 s.

[0128]FIGS. 17 and 18 show other examples relating to a damasceneprocess. FIGS. 17a) to 17(e) show a process that processes a groovefirst, and FIGS. 18(a) to 18(e) show a process that processes a holefirst. The difference between these two processes is only whether a holeis processed first or a groove is processed first, and the details ofthe application of this invention are the same as described above. Ineither case, oxide film 302, low-k film 303, silicon nitride film 304,low-k film 305, silicon nitride film 306, and begging 307, which becomeswiring of the lower layer are formed.

[0129] In FIG. 17(a), initially, resist mask 301 for processing a grooveis formed by exposure development, and then groove 308 is formed byetching oxide film 302 and low-k film 303 by plasma etching, as seen inFIG. 17(b). At this time, etching stops at silicon nitride layer 304,which is a stopper layer equivalent to the bedding of low-k film 303.Then, hole 310 is formed through exposure development by applying resistmask 309, applying plasma etching, as seen in FIG. 17(c), and removingresist mask 309, as seen in FIG. 17(d). Finally, silicon nitride film306 is etched to effect contact with bedding 307, as seen in FIG. 17(e).Then, wiring is formed by inserting a wiring material such as aluminumor copper in the opening section (310) and smoothing the upper section.

[0130] As shown in FIG. 18(a), resist mask 301 for processing a hole isformed by exposure development, and then hole 310 is formed by etchingthe oxide film and the low-k film using plasma etching, as seen in FIG.18(b). In this case, etching stops at silicon nitride film 306 of thestopper layer that is equivalent to the bedding of low-k film 305.Exposure development is applied to resist mask 311 for processing agroove, as seen in FIG. 18(c), and groove 308 is formed by removing theresist mask through plasma etching, as seen in FIG. 18(d). Finally,silicon nitride film 306 is etched to effect contact with bedding 307,as seen in FIG. 18(e). Then, wiring is formed by inserting a wiringmaterial such as aluminum or copper in the opening section and smoothingthe upper section.

[0131] The damascene process as shown in FIGS. 17(a) to 17(e) and 18(a)to 18(e) enable startup of an end point judging system in a short time.Consequently, by implementing a specified over-etching by judging theetching end point up to the silicon nitride film using this system,excessive etching on a thin film such as a stopper layer can becontrolled, resulting in high precision etching results.

[0132] FIGS. 19(a) to 19(f) show the dual damascene process when siliconnitride film 202, which is a stopper layer shown in FIG. 16, is notformed. The process involves etching of the following; resist 401, inwhich a mask for processing a hole is formed, as seen in FIG. 19(a),oxide film 402, low-k film 403, silicon nitride film 404, and the layerin which bedding 405 is formed. Initially, hole 406 that reaches siliconnitride film 404 is formed on low-k film using plasma etching, as seenin FIG. 19(b). Then, resist is applied and exposure development isapplied to form resist 407 where a mask for processing a groove isformed, as seen in FIG. 19(c). Etching stops when a groove of thespecified depth is formed on low-k film 403. Since low-k film 403 isuniform, it is not possible to judge, as an end point, the point whereetching has reached the silicon nitride film. Therefore, by measuringthe etching speed in advance and managing the etching time, etching isprocessed to the depth of the groove. In this case, strict etching speeduniformity within the wafer surface and repeatability are required.

[0133] As the end point judging system of this invention, by using ahigh precision system that can start measurement preparation in a shorttime and can judge end points in a short interval and a system that canjudge minimal changes (fluctuation of minimal etching characteristics)of plasma, the following method is enabled, resulting in more precisegrooving processing. That is, the low-k film structure shown in FIG.20(a) is introduced. The structure is formed by oxide film 501, low-kfilm 502, boundary face 503, low-k film 504, silicon nitride film 505,and bedding 506. In this case, low-k film 502 and low-k film 504 are lowdielectric materials of different film types. It is important to formboundary face 503 between low-k film 502 and low-k film 504 by usingfilms of slightly different specifications when the films are of thesame type, by exposing low-k film 504 to the atmosphere by interruptingthe film forming after the film is formed, or by applying a processwhose surface state is different from the bulk. In this structure,although boundary face 503 is formed, a low dielectric constant can bemaintained because all the film components are made of low dielectricmaterials.

[0134] As the next step, the film is etched by plasma etching. Thedescription of the mask materials is omitted because they are the sameas used for the process of FIGS. 19(a) to 19(f). After starting from thegroove processing in FIG. 19, the etching characteristics of the bulkand boundary surface 503 become slightly different when the groove depthreaches boundary surface 503. The time required for etching to reachboundary face 503 can be judged using the end point judging system ofthis invention. Therefore, when etching ends at this point, a dualdamascene structure that does not insert silicon nitride in the stopperlayer with the groove depth of the boundary face 503 is completed. Theperformance required for the end point judgment is not only detection ofminimal changes of plasma at high precision, since etching on boundarysurface ends in a very short time, but also judgment of the amount ofchange by measuring the plasma emission in a short time interval. Theend point judging system of this invention can satisfy theserequirements. The numeral 508 denotes a hole for contact with bedding506.

[0135] An example of applying this invention to self-alignment contacttechnology will be described below. FIG. 21 shows a pre-etching crosssection of a self-alignment contact and FIG. 22 shows a post-etchingcross section. The conventional contact holes are arranged at a slightlyshorter distance than the distance between gates in order to resolve adrift at matching of the lithography position. As shown in FIGS. 21 and22, since an insulation film is formed on the top and side of a gate inthe self-alignment contact structure, the gate is protected by theinsulation film even if the contact hole overlaps on the gate.Therefore, since a greater lithography position drift can be provided, ashorter distance between gate polarities becomes possible.

[0136] The structure of the self-alignment contact shown in FIG. 21comprises resist 601, oxide film 602, such as TEOS or BPSG, oxide film603, such as SOG, silicon nitride film 604, bedding 605, and gate 606.The area of gate 606 is the final contact area, and in the filmstructure of this example, the bottom of the hole 607 is formed insilicon nitride film 604. Therefore, a process for removing siliconnitride film 607 is required after etching of the oxide film 602 iscompleted. For plasma etching of a self-alignment contact film, sincethe process using a CF gas has been developed and many research examplesare reported regarding the etching characteristics, a description of theetching is omitted in this document.

[0137] As shown in FIG. 22, the problems of etching are noticeablecorrosion on the bottom of the hole in the resist (corresponds to 607)and corrosion of the shoulder section 608 of the silicon nitride film604. In particular, when an oxide film is etched repeatedly, thetemperature on the wall in the etching chamber fluctuates, thedeposition characteristics of the etching gas and etching residue on theinside wall fluctuate, or the gas discharge behavior changes. As aresult, etching characteristics are changed and sometimes etching downto the bedding is disabled. This phenomenon is called etch stop. Whenetch stop occurs, a large number of device faults occur. Therefore, etchstop must be definitely prevented. Detection of etch stop is alsoimportant.

[0138] When the end point judging system of this invention is used, hightime precision for detecting minimal etching characteristic fluctuationscan be achieved since the system can measure in a short time changes ofplasma emission, that is, the plasma change measuring time interval isshort. The time required for etching from the start of etching in thestate shown in FIG. 21 to reaching the upper face of oxide film 603(boundary face between oxide film 602 and oxide film 603), is determinedthrough progress of etching on oxide film 602. The etching speed isobtained using this data and the thickness of the oxide film 602 thathas been measured, and the result is recorded and stored as etchingspeed data for oxide film 602. By comparing the etching speed data forthe previous etching and this data, changes in the passage of time ofthe etching device can be obtained. The yield can be improved bydisplaying the data on the control panel of the etching device andchecking the stability of the device during production.

[0139] The method of this invention can also be applied for monitoringstable operation of the device since the method enables measurement ofspeed easily during etching processing. The next step is to etch anarrow area between gates by etching oxide film 603. The etching speedobtained by the method described above can also be used as the base datafor improving the selection ratio by retarding etching of the shouldersection 608 or determining the over-etching time after etching reachesthe bottom of the hole 607 of silicon nitride film 604. In addition, byobtaining the etching speed of oxide film 603 between gates in the samemethod, the data can be used for verifying the stability of etchingcharacteristics or detection of etch stop. Even if the film thickness isnot available in advance, the stability of etching characteristics inthe lot can be verified by checking the degree of changes of etchingtime for each wafer. As described above, the data can also be constantlymonitored by displaying it on the controller of the device and can beused for determining timing of changing the process condition or timingof full sweep.

[0140] Another example of this invention shows utilization of featuresof the quick measurement preparation and the short end point judgmentinterval. An end point is judged with a high precision in a short timeby using the end point judging system of this invention in the casewhere a contact between the lower section (bedding 605) and the uppersection is formed by removing silicon nitride 604 by etching so as tocomplete etching of self-alignment contact, as shown in FIG. 22. Sincethe bottom 607 of the silicon nitride film 604 is very thin, bedding 605may be excessively etched unless a correct etching end point is judged.Since the etching time is short (10 and several seconds), the set plasmameasurement preparation time must be shorter than usual. By using theend point judging system of this invention, the end point can be judgedeasily.

[0141] In the example shown in FIG. 1, emission of a specific wavelengthfrom the plasma generated within chamber 2 is obtained by spectroscope12; however, the same result can be achieved by passing a light of thearea of the specific wavelength and using an optics filter that shutsout the light of other wavelength areas or dramatically attenuates thelight, instead of using spectroscope 12.

[0142] In the example shown FIG. 1, a spectroscope and aphoto-multiplier are used. However, as described in JapaneseNon-examined Patent Publication 59-18424, by digitizing the signalscorresponding to multi-wavelengths through an AD modulator, using aslit, grading, and line sensor, the data can be stored in a storage unitin a specified cycle, or data corresponding to the required wavelengthcan be fetched in a specified cycle. This system has an advantage ofbeing able to set a required wavelength electronically.

[0143] When a slit, grading, or a line sensor is used and a longinterval is set for a scan start signal of the line sensor, theaccumulated electric charge is increased, increasing the size of theoutput signal. To prevent this phenomenon, automatic gain adjustment isenabled by monitoring the size of the signal output from the line sensorand adjusting the interval of the scan start signal of the line sensorso that the maximum value is set to a specified value.

[0144] When the number of elements of the line sensor is insufficientfor the required wavelength precision, the wavelength precision can beimproved by internal insertion.

[0145] Characteristic irregularity in this system results inirregularity of wavelengths of the light that forms spectra to thelinear sensor side. Therefore, wavelengths corresponding to the datastored in the storage unit that was described above can be calibrated byallowing input of light from a standard light source for calibrationthat has known optical spectrum in addition to the light from thechamber as the light to be input to a slit (for instance, using dualfibers) and setting the standard light source for calibration to ONperiodically.

[0146] This example shows judgment of an etching end point using plasma,however, the method is also effective for judging a cleaning end pointusing plasma so that the method can be used for judging end points ofplasma cleaning after etching processing or after plasma CVD. That is,the method can be applied for judging end points of plasma processingand has the following features.

[0147] (1) Plasma processing end point judging device with the followingfeatures in plasma processing end point judgment using emissionspectrometry: an AD conversion method for obtaining emission intensitytime series data of a specific wavelength, a first digital filteringmethod for smoothing processing of the time series data, a differentialoperation method for obtaining a differential coefficient of thesmoothed time series data, a second digital filtering method forsmoothing processing of time series data of the calculated differentialcoefficient, and a discrimination method for judging an end point ofplasma processing by comparing the smoothed differential coefficientvalue and the preset value.

[0148] (2) Plasma processing end point judging device with the followingfeatures in the plasma processing end point judging device describedabove: a method for detecting a plasma processing abnormality, a firstdigital filtering correction method that corrects the smoothed timeseries data at detection of an abnormality and the time series data ofthe differential coefficient, and the smoothed differential coefficienttime series data, differential operation correction method, and a seconddigital filtering correction method.

[0149] (3) Plasma processing end point judging device with the followingfeatures in the method of judging plasma processing end points from timeseries data of emission intensity differential coefficient: a method fordisplaying a transition of times series data of the differentialcoefficient described above and a method for displaying an abnormalityon the time series data display of the differential coefficientdescribed above at detection of an abnormality.

[0150] The etching method of this invention can calculate emissionintensity changes with a high precision. Consequently, an etching endpoint detection method that uses this feature can provide a very stableetching processing end point judgement.

[0151] This invention enables determination of a correct sense voltagevalue for a target output voltage of a photo-multiplier by obtaining andusing a sense voltage value for a target output voltage of aphoto-multiplier through a relational expression. Therefore, even for asemiconductor wafer having a small opening ratio, this invention canprovide a method of controlling the signals used for repeatedlydetecting etching end points within a constant value withoutirregularity between wafers for stable detection of etching end pointsof semiconductor wafers.

[0152] By using this invention, the noise of sampling signals from alight detector can be reduced effectively, enabling stable end pointjudgment by setting digital filtering processing before and afterdifferential coefficient calculation processing in end point judgmentfor differential coefficient calculation processing for judging endpoints. By providing coefficient correction processing in the digitalfiltering processing of the prior stage, differential coefficientcalculation processing, and digital filtering processing of the poststage, noise of sampling signals from a light detector can be reducedmore effectively, enabling stable and high-precision end point judgment.In addition, in a differential coefficient display, by drawing on thezero or a preset display position using a specific color arrangement atthe time of an etching processing abnormality, an effective device forfacilitating abnormality monitoring during etching can be provided.

[0153] This invention enables accurate execution of end point judgmentso that low over etching can be set in comparison to the etching managedby time. As a result, excessive corrosion of the bedding layer can becontrolled. In addition, an over etching time can be reduced, resultingin improvement of the throughput. Since changes can be monitored in thepassage of time, an etching device abnormality can be detected at anearly stage, preventing a large number of etching faults.

What is claimed is:
 1. An etching end point judging device usingemission spectroscopy for dry etching, wherein said device comprises A/Dconversion means for obtaining time series data of emission intensity ofa specific wavelength produced during etching, first digital filteringmeans for performing smoothening of said time series data, differentialoperation means for obtaining a differential coefficient of saidsmoothened time series data, second digital filtering means forsmoothening the calculated differential coefficient of said time seriesdata, and discrimination means for judging the etching end point bycomparing said smoothened differential coefficient with a value setbeforehand.
 2. An etching end point judging device according to claim 1,wherein said device further comprises means for detecting abnormalitiesin the etching process, first digital filtering correction means thatcorrects—in the event of detection of any abnormality—said smoothenedtime series data, said differential coefficient time series data, andsaid smoothened differential coefficient time series data, correctionmeans for correcting said differentiation operation, and second digitalfiltering correction means.
 3. An etching end point judging device thatjudges the end point of etching from a time series data of adifferential coefficient of light emission intensity, wherein saiddevice comprises display means that displays a transition of said timeseries data of said differential coefficient, and means for displayingan abnormality in the display of said time series data display of saiddifferential coefficient in the event of detection of any abnormality.4. An etching end point judging device according to claim 1, whereinsaid device further comprises a photo-electronic photo-multiplier tubethat outputs a current value that indicates the intensity of light of aspecific wavelength that is emitted during etching carried out by aplasma discharge, an I/V converter that converts the current valueoutput by the photo-multiplier tube into a voltage value, an A/Dconverter that digitizes the offset and gain for processing the outputvoltage from the I/V converter and the output from the output and gainof the IN converter, sense adjustment means that obtains from the datadigitized in the A/D converter a sense voltage value for using theoutput of the photo-multiplier tube as a target output, dark currentcalculation means for determining the dark current of thephoto-multiplier tube, gain correction means for changing the gain thatis normally used as a fixed value in the event there is an overflow inthe obtained sense voltage value, a D/A converter that converts thesense voltage value, offset value, and gain value that were obtainedinto analog data and sets the data.